Polyesters such as polyethylene terephthalate (PET) are known to possess good chemical stability, physical and mechanical strength, durability, heat resistance, chemical resistance, weather resistance and electrical insulation property and, therefore, have been widely used in manufacturing various articles including medical devices, capacitors, packaging and labelling materials, photographic film and magnetic recording media.
Recently, an increasing amount of polyester resins has been used in laminating inner surface of metal containers such as cans because they can be conveniently laminated to a metal surface without the use of any solvent. However, a conventional polyester resin generally has poor adhesiveness, and therefore, it requires an adhesive in such a laminating process. The use of an adhesive however causes the problem of a high production cost and the risk of contaminating the content. Moreover, a conventional polyester film tends to have a high crystallization degree and the processability thereof is poor, i.e., it may be torn or broken in a further processing step.
In order to solve such problems, U.S. Pat. No. 5,424,121 discloses the use of a polyester copolymer having good thermal adhesive strength and low crystallinity in laminating a food container. However, a film prepared from this polyester copolymer has the disadvantages that it has low thermal stability and that the laminate is easily deformed and discolored by thermal oxidation.